Archery sights have long been available for use when the bow is held vertically and when the archer and the target are on the same level. As an example of a modern archery sight, please see U.S. Pat. RE 36,266 (“Bow Sight”).
However, these conditions are not always met in the field. First, while archers have long been told to hold their bows in a vertical plane, this orientation is not entirely natural to the human arm. Holding the bow in this vertical position places some rotational stress on the arm. “Canting” the bow, that is, holding it at a slight angle from the vertical plane, feels more natural and reduces the stresses acting on the archer and on the bow thus leading to more accurate shots.
Second, and relatedly, archers in some situations tend to change the cant at which they hold their bow. This change is noticeable when the archer and the target are not on the same level. While hunting in rough terrain, for example, the archer's best (or only) shot often presents itself when the target is either above or below the archer's level. When moving the bow to aim at a target above or below the archer's own position, the archer tends to change the cant of the bow. When using a traditional archery sight, this unconscious change in cant results in shots hitting to the right or left of the target.
For these and other reasons, there is a need for an archery sight that compensates for conditions beyond the idealized conditions of the archery range.